Oh, I love playing Internet Gotcha!
Masterson pitched great last night, to my pleasant surprise. He looked like crap in the minors before that start; last night's start doesn't change that fact.
Lowrie doesn't look like he has the range to be a full time major league SS to me. Maybe I'm wrong; it wouldn't be the first time and it won't be the last.
For what it's worth, here's my take on the Red Sox shortstops.
I would be shocked if the Red Sox made Lowrie their full-time SS. This team seems to value defense at SS quite a bit (Nomar, Rentaria), and from what I can see, Lowrie gets a bad jump on balls (almost seems to take a few baby steps before getting going, like Fred Flinstone in his car) which limits his range. He also has weird footwork on some of his throws, taking multiple hop steps before releasing the ball.
Concerning Lugo and Cora, I suspect this is a temporary arrangement caused by Lugo's mental troubles in the field and, possibly, his concussion. I concur with the majority here that Lugo has better range to either side, comes in on balls better, and is about even with Cora going back on pop-ups (neither is great). Lugo also has a stronger arm. Cora has better hands, a much more accurate arm, and, most importantly for the time being, does not get the "yips" in the field which Lugo is prone to do.
Cora's defensive evaluations are all over the place, with one, The Hardball Times, listing Cora as one of only 14 players in MLB to get an A+ grade . One huge problem (and there are others) with this type of evaluation is that the sample size is just too small for Cora, a part time player. With a limited number of chances per season, and with so many of them routine, it really takes 3 seasons of full-time data for a defensive evaluation to be legit, in my opinion. THT correctly does use three years of data for their defensive evaluations, but Cora only played only 882 innings at SS over 2005 - 2007, the equivalent of 98 full games, and not nearly enough to make a definitive judgment on his defensive ability. Overall, Cora had 1660 defensive innings over the three seasons at 2nd, SS, and 3rd, or just over one full time season.
One last point in this rambling post, AL SS's thus far in 2008 have posted a pathetic cumulative OPS of .656, which makes Lugo (.680) a better than average offensive SS thus far this season.